The present invention relates to an image display apparatus and a method of driving the image display apparatus, particularly, to an image display apparatus constituted by commonly wiring a plurality of display devices and a driving method thereof, more particularly, to an image display apparatus having a display panel constituted by wiring a plurality of display devices in a matrix and a driving method thereof and, still more particularly, to an image display apparatus capable of displaying a television signal and computer video signal with high quality and a driving method thereof.
Conventionally, two types of devices, namely thermionic and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction type emission devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example of the surface-conduction type emission devices is described in, e.g., M. I. Elinson, xe2x80x9cRadio E-ng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction type emission device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction type emission device includes electron-emitting devices using an Au thin film (G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)), an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)), a carbon thin film (Hisashi Araki et al., xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)), and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 11 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction type emission devices. Referring to FIG. 11, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering.
This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 11. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 11 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction type emission devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electronemission. In forming processing, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after forming processing, electrons are emitted near the fissure.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField Emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical Properties of Thin-Film Field Emission Cathodes with Molybdenium Conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
FIG. 12 is a sectional view showing the device by C. A. Spindt et al. described above as a typical example of the FE type device structure. In FIG. 12, reference numeral 3010 denotes a substrate; 3011, an emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, a gate electrode. In this device, a voltage is applied between the emitter cone 3012 and gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012.
As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 12.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961). FIG. 13 shows a typical example of the MIM type device structure. In FIG. 13, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 xc3x85; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 xc3x85. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper and lower electrodes 3023 and 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above-described cold cathode devices can emit electrons at a temperature lower than that for thermionic cathode devices, they do not require any heater. The cold cathode device has a structure simpler than that of the thermionic cathode device and can shrink in feature size. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the thermionic cathode device is low because the thermionic cathode device operates upon heating by a heater.
For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the surface-conduction type emission devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the assignee of the present application, a method of arranging and driving a lot of devices has been studied.
Regarding applications of the surface-conduction type emission devices to, e.g., image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like have been studied.
Particularly, as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the assignee of the present application, an image display apparatus using a combination of a surface-conduction type emission device and a fluorescent substance which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus using a combination of the surface-conduction type emission device and fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, compared with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because it is of a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the assignee of the present application. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat panel display reported by R. Meyer et al. (R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)).
An application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the assignee of the present application.
It is an object of the present invention to realize an image display apparatus capable of displaying various kinds of signals with high quality in an arrangement in which a plurality of display devices are commonly wired, and a driving method thereof.
One aspect of an image display apparatus according to the present invention comprises the following arrangement.
An image display apparatus comprises a row wiring, a plurality of column wirings, a modulator, and a plurality of display devices, the plurality of display devices being commonly connected to the row wiring, each of the plurality of column wirings being connected to a corresponding one of the plurality of display devices, and the modulator supplying a modulated signal to the column wirings,
wherein the modulator includes a pulse width modulator for generating a pulse signal having a time width corresponding to a tone of a signal to be displayed, and a potential setting circuit for setting a potential of the pulse signal in accordance with a type of signal to be displayed.
The pulse width modulator and potential setting circuit, or the modulator including them may be one integrated circuit. The modulator and another circuit may be integrated into one.
The potential of a pulse signal having a modulated time width may be adjusted by the potential setting circuit. Alternatively, a pulse width signal having a modulated time width may be generated at a potential set in advance by the potential setting circuit. This aspect incorporates both the arrangements. Note that the potential to be applied to the column wiring is set while a predetermined signal is supplied to the row wiring and the plurality of display devices can be driven. In particular, when a high-level period is to be changed in pulse width modulation, a high-level potential is set. In this case, the xe2x80x9chigh levelxe2x80x9d of the signal means a level corresponding to a signal which drives the device or a signal for a high driving state, with respect to a low level corresponding to a signal which does not drive the device or a signal for a low driving state. Low- and high-level signals do not always have lower and higher potentials, respectively.
According to this aspect, the tone is controlled by the pulse width of a pulse signal, and control corresponding to the type of signal to be displayed is executed by controlling the potential of a pulse signal. The influence on tone control caused by control corresponding to the type of signal to be displayed can be preferably suppressed.
In this aspect, a longitudinal direction of the column wiring preferably crosses a longitudinal direction of the row wiring.
In each aspect, it is preferable that the row wiring include a plurality of row wirings, a plurality of display devices be connected to each row wiring, and each of the plurality of display devices connected to the row wiring share a corresponding column wiring with each of a plurality of display devices connected to another row wiring.
This includes so-called matrix wiring. The matrix wiring has a plurality of row wirings, a plurality of column wirings extending to cross the row wirings, and display devices arranged in correspondence with the intersections of the row and column wirings. Each display device may be arranged at or near the intersection. The display device is connected at a corresponding intersection to row and column wirings crossing each other.
The image display apparatus preferably further comprises a scanning circuit for supplying a scan signal for sequentially scanning the plurality of row wirings. As the scanning circuit, this aspect can preferably employ a circuit for applying a selection potential to a selected row wiring. This aspect can preferably adopt an arrangement in which the display device is driven by a voltage applied to it owing to the difference between the selection potential and the potential of a pulse signal supplied to the column wiring. A predetermined non-selection potential is preferably applied to an unselected row wiring.
The above aspect can be preferably applied when the display device consumes only part of a current flowing into the display device for display.
In this arrangement, a current (particularly, a current not consumed by the display device for display) flows through the row wiring to increase the influence of the voltage drop on the row wiring which applies the potential to one end of each of a plurality of simultaneously drivable devices. This arrangement can preferably adopt the aspect of the present invention in which the pulse width can be adjusted in accordance with the type of signal. The present invention is effective in an arrangement in which a row wiring commonly connected to a plurality of simultaneously drivable display devices flows even a small current which is not consumed by the display device for display. The present invention is especially effective when 20% or more of a current flows into the display device, and more preferably 50% or more of the current flows through the column or row wiring without consuming the current for display. For example, most of surface-conduction type emission devices (to be described later in the following embodiments) consume about less than several % of a flowing current for emission. Most of EL devices known as display devices consume about several ten % of a flowing current for emission. In either case, the present invention can be preferably applied. Note that the current consumed by the display device for display includes a current consumed as heat in display operation.
Each aspect can preferably employ an arrangement in which the apparatus further comprises a plurality of input portions for inputting an image signal to be displayed, and a selector for selecting any one of signals from the plurality of input portions, and the potential setting circuit sets the potential of the pulse signal in accordance with a selection state of the selector, an arrangement in which the apparatus further comprises a discrimination circuit for discriminating a characteristic of an image signal to be displayed, and the potential of the pulse signal is set in accordance with a discrimination result of the discrimination circuit, or an arrangement in which the apparatus further comprises external setting means for setting the potential of the pulse signal in accordance with an image to be displayed, and the potential setting circuit sets the potential of the pulse signal in accordance with a setting of the external setting means.
In each aspect, the potential setting circuit desirably sets the potential in accordance with whether importance is attached to luminance or reproducibility in displaying an input image signal. When luminance is more important than reproducibility in displaying an input image signal, the potential set by the potential setting circuit is desirably set to have a larger potential difference from a potential applied to the row wiring than when reproducibility is more important than luminance.
In each aspect, the potential setting circuit preferably sets the potential of the pulse signal in accordance with whether the signal to be displayed is a computer image signal or a television image signal. More specifically, when the computer image signal is to be displayed, the potential of a pulse signal is set to have a smaller potential difference from a potential applied to the row wiring than when the television image signal is to be displayed.
Another aspect of an image display apparatus according to the present invention comprises the following arrangement.
An image display apparatus comprises a row wiring, a plurality of column wirings, a modulator, and a plurality of display devices, the plurality of display devices being commonly connected to the row wiring, each of the plurality of column wirings being connected to a corresponding one of the plurality of display devices, and the modulator supplying a modulated signal to the column wirings,
wherein the modulator includes a potential setting circuit for setting a potential of a signal supplied to the row wiring in accordance with a type of signal to be displayed.
This arrangement can preferably realize control corresponding to the type of image signal displayed by a signal supplied to the row wiring, independently of modulation control using a signal supplied to the column wiring. In this aspect, the modulator can adopt an arrangement of generating a pulse width-modulated signal having a time width corresponding to the tone of a signal to be displayed, and an arrangement of generating a peak value-modulated signal having a peak value corresponding to the tone of a signal to be displayed. The pulse width modulating arrangement is more desirable in terms of tone display.
Also in this aspect, a longitudinal direction of the column wiring preferably crosses a longitudinal direction of the row wiring. This aspect can preferably be applied to an arrangement in which the row wiring includes a plurality of row wirings, a plurality of display devices are connected to each row wiring, and each of the plurality of display devices connected to the row wiring shares a corresponding column wiring with each of a plurality of display devices connected to another row wiring.
The image display apparatus desirably further comprises a scanning circuit for supplying a scan signal for sequentially scanning the plurality of row wirings. More specifically, the scanning circuit can preferably adopt an arrangement of applying a selection potential to a selected row wiring. In this arrangement, the selection potential is set in accordance with the type of image signal to be displayed.
Still another aspect of an image display apparatus according to the present invention comprises the following arrangement.
An image display apparatus comprises a row wiring, a plurality of column wirings, a modulator, and a plurality of display devices, the plurality of display devices being commonly connected to the row wiring, each of the plurality of column wirings being connected to a corresponding one of the plurality of display devices, and the modulator supplying a modulated signal to the column wirings,
wherein the modulator includes a peak value modulator for generating a signal having a peak value corresponding to a tone of a signal to be displayed, and a peak value setting circuit for setting an upper limit of the peak value in accordance with a type of signal to be displayed.
In this aspect, the upper limit of the peak value is relative. When modulation is done such that the potential of a signal corresponding to a high tone is set high, and the potential of a signal corresponding to a low tone is set low in controlling the peak value of a signal by controlling the potential of the signal, the upper value of the peak value is the upper limit of the potential. When modulation is done such that the potential of a signal corresponding to a high tone is set low, and the potential of a signal corresponding to a low tone is set high, the upper limit of the peak value is the lower limit of the potential. In this aspect, the minimum value of the amplitude of the peak value may also be set.
The above aspects of the present invention are preferable when the display device consumes 80% or less of a current flowing into the display device for display, and more preferable when the display device consumes 50% or less of a current flowing into the display device for display.
In the above-described aspects, the display device is, e.g., an electron-emitting device. This electron-emitting device is desirably used in combination with an emission substance (especially, a fluorescent substance) for emitting light upon irradiation of electrons emitted by the electron-emitting device. As the electron-emitting device, a cold cathode device can be preferably employed. The present invention is more preferable in an arrangement using a surface-conduction type emission device. When the display device is an electron-emitting device, an image can be displayed with high quality using a fluorescent substance for emitting light upon irradiation of electrons emitted by the electron-emitting device.
Even when the display device is an electroluminescent device, the above aspects can be preferably used. When the display device is an electroluminescent device, since the device itself emits light, it is preferable.
One aspect of a method of driving an image display apparatus according to the present invention is as follows.
A method of driving an image display apparatus having a row wiring, a plurality of column wirings, a modulator, and a plurality of display devices, the plurality of display devices being commonly connected to the row wiring, each of the plurality of column wirings being connected to a corresponding one of the plurality of display devices, and the modulator supplying a modulated signal to the column wirings, comprises the step of
applying to the column wiring a pulse width-modulated signal having a potential set in accordance with a type of signal to be displayed and a time width corresponding to a tone of the signal to be displayed, thereby modulating the display device.
Another aspect of a method of driving an image display apparatus according to the present invention is as follows.
A method of driving an image display apparatus having a row wiring, a plurality of column wirings, a modulator, and a plurality of display devices, the plurality of display devices being commonly connected to the row wiring, each of the plurality of column wirings being connected to a corresponding one of the plurality of display devices, and the modulator supplying a modulated signal to the column wirings, comprises the step of
setting a potential of a signal supplied to the row wiring in accordance with a type of signal to be displayed.
Still another aspect of a method of driving an image display apparatus according to the present invention is as follows.
A method of driving an image display apparatus having a row wiring, a plurality of column wirings, a modulator, and a plurality of display devices, the plurality of display devices being commonly connected to the row wiring, each of the plurality of column wirings being connected to a corresponding one of the plurality of display devices, and the modulator supplying a modulated signal to the column wirings, comprises the steps of
generating a signal having a peak value corresponding to a tone of a signal to be displayed, and
setting an upper limit of the peak value in correspondence with a type of signal to be displayed.
Note that the above-mentioned aspects are more preferable when the modulator outputs a potential-controlled signal (e.g., high-level potential) as a control target than when the modulator outputs a current-controlled signal as a control target.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.